linux-kernel - Re: [PATCH] ext4: address a benign compiler warning

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Date:	Wed, 12 Feb 2014 18:59:42 -0800
From:	Joe Perches <joe@...ches.com>
To:	Patrick Palka <patrick@...cs.ath.cx>
Cc:	linux-kernel@...r.kernel.org, tytso@....edu,
	adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: address a benign compiler warning

On Wed, 2014-02-12 at 21:13 -0500, Patrick Palka wrote:
> When !defined(CONFIG_EXT4_DEBUG), mb_debug() should be defined as an
> empty do-while statement so as to suppress the following compiler
> warning:

Hello Patrick.

> fs/ext4/mballoc.c: In function ‘ext4_mb_cleanup_pa’:
> fs/ext4/mballoc.c:2659:47: warning: suggest braces around empty body in an ‘if’ statement [-Wempty-body]
>    mb_debug(1, "mballoc: %u PAs left\n", count);
> ---
> diff --git a/fs/ext4/mballoc.h b/fs/ext4/mballoc.h
[]
> @@ -48,7 +48,7 @@ extern ushort ext4_mballoc_debug;
>  		}							\
>  	} while (0)
>  #else
> -#define mb_debug(n, fmt, a...)
> +#define mb_debug(n, fmt, a...)		do { } while (0)

Ideally, this section should be something like below
so the !CONFIG_EXT4_DEBUG case still verifies that
the format and argument types match.

This can help avoid people adding debug statements but
not compiling with the proper CONFIG_<foo> variable set.

---

#ifdef CONFIG_EXT4_DEBUG
extern ushort ext4_mballoc_debug;

#define mb_debug(n, fmt, ...)					\
do {								\
	if ((n) <= ext4_mballoc_debug)				\
		pr_debug(fmt, ##__VA_ARGS__);			\
	}							\
} while (0)
#else
#define mb_debug(n, fmt, ...)					\
	no_printk(KERN_DEBUG fmt, ##__VA_ARGS__)
#endif


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